This invention relates to a semiconductor wafer and a vapor phase growth apparatus and particularly, a semiconductor wafer obtained by forming a semiconductor thin film having a uniform resistivity distribution on a main surface of a large diameter semiconductor single crystal substrate and a vapor phase growth apparatus employed for producing the semiconductor wafer.
In company with recent miniaturization of an electronic device, not only has the use of semiconductor wafers each obtained by forming a silicon single crystal thin film on a main surface of a silicon single crystal substrate increased, but a more uniform resistivity distribution of the silicon single crystal thin film has also been required. The term xe2x80x9cuniform resistivity distributionxe2x80x9d used here, to be detailed, means that a resistivity distribution across the surface of the silicon single crystal thin film is uniform. Further, a larger diameter has also been demanded on a semiconductor wafer together with the uniform resistivity distribution. A horizontal, single wafer vapor phase growth apparatus has been mainly employed as an apparatus for growing a silicon single crystal thin film on a main surface of a silicon single crystal substrate keeping pace with use of a large diameter semiconductor wafer.
Description will be below given of a horizontal, single wafer vapor phase growth apparatus generally employed with reference to FIGS. 5 and 6, wherein FIG. 5 is a sectional view in a horizontal plane showing a conventional horizontal, single wafer vapor phase growth apparatus in a simplified manner and FIG. 6 is a vertical sectional view showing the apparatus in a simplified manner.
As shown in FIGS. 5 and 6, in a conventional horizontal, single wafer vapor phase growth apparatus, a susceptor 14 on which a silicon single crystal substrate 12 is horizontally placed is disposed at the bottom of the middle portion of a transparent quartz glass reaction chamber 10 installed along a horizontal direction and the susceptor 14 is coupled with a rotation unit (not shown) through a rotary shaft 16.
Further, a gas inlet port 18 is provided at one end in a length direction of the reaction chamber 10 and a gas outlet port 20 is provided at the other end thereof. With this construction, a flow of a gas which is introduced through the gas inlet port 18 into the reaction chamber 10 and discharged through the gas outlet port 20 to the outside passes over a main surface of the silicon single crystal substrate 12 placed on the susceptor 14 almost along a length direction of the reaction chamber 10. Further, the gas inlet port 18 of the reaction chamber 10 is constructed of six inlet ports 18a to 18f spread in a width direction of the reaction chamber 10. Among the six inlet ports 18a to 18f, a pair of two inlet ports at the innermost side (hereinafter simply referred to as inner inlet ports) 18a and 18b are arranged in symmetry with respect to an imaginary central axis along a length direction of the reaction chamber 10, passing through the center of the main surface of the silicon single crystal substrate 12 on the susceptor 14, and this arrangement of the inner inlet ports 18a and 18b applies to not only a pair of two inlet ports at the outermost side (hereinafter simply referred to as outer inlet ports) 18e and 18f, but also a pair of two inlet ports each between one of the two inner inlet ports and the corresponding one of the two outer inlet ports (hereinafter simply referred to as middle inlet ports) 18c and 18d in the same way.
To be more detailed, the inner inlet ports 18a and 18b are directed toward points in the vicinity of the center of the main surface of the silicon single crystal substrate 12 on an imaginary central axis along a width direction of the reaction chamber 10, passing through the center of the main surface of the silicon single crystal substrate 12 on the susceptor 14, and the outer inlet ports 18e and 18f are directed toward points in the vicinity of the outer periphery of the main surface of the silicon single crystal substrate 12 on the imaginary central axis line and the middle inlet ports 18c and 18d are directed toward points between the central portion and the outer peripheral portion of the main surface of the silicon single crystal substrate 12 on the imaginary central axis line.
Further, the six inlet ports 18a to 18f are all connected to a common gas pipe 22. The common gas pipe 22 are branched in three ways and the branches are connected to a gas source (not shown) of hydrogen (H2) gas as a carrier gas, a gas source (not shown) of a semiconductor raw material gas and a gas source (not shown) of a dopant gas through mass flow controllers MFC 24, 26 and 28, respectively, as gas flow rate regulators.
Further, outside of the reaction chamber 10, an infrared radiation lamp 30, for example, as a heat source heating the silicon single crystal substrate 12 placed on the susceptor 14 is disposed and by supplying a power to the infrared radiation lamp 30, the main surface of the silicon single crystal substrate 12 is heated to a predetermined temperature. In addition, cooling means (not shown) for cooling the infrared radiation lamp 30 and an outer wall of the reaction chamber 10 is equipped and thus, a so-called cold-wall vapor phase growth apparatus is constituted. In the cold-wall vapor phase growth apparatus, since the outer wall surface of the reaction chamber 10 is forcibly cooled, deposits composed mainly of silicon on the inner wall surface of the reaction chamber 10 can be prevented from forming.
Then, description will be made of a method for forming a silicon single crystal thin film on the main surface of the silicon single crystal substrate 12 using the conventional horizontal, single wafer vapor growth apparatus shown in FIGS. 5 and 6. First, the silicon single crystal substrate 12 is horizontally placed on the susceptor 14 of the reaction chamber 10. Following this, H2 gas is supplied into the reaction chamber 10 from the gas source of H2 gas through MFC 24, the common gas pipe 22 and through the six inlet ports 18a to 18f to replace the atmosphere in the reaction chamber 10 with hydrogen. Further, with the rotation device, the susceptor 14 is rotated through the rotary shaft 16 clockwise as shown by arrow marks of FIGS. 5 and 6 while the silicon single crystal substrate 12 is horizontally placed on the susceptor 14. Then, with the infrared radiation lamp 30, the silicon single crystal substrate 12 on the susceptor 14 is heated to raise a temperature of the main surface thereof to a predetermined one.
After doing so, the semiconductor raw material gas and the dopant gas are supplied into the reaction chamber 10 from the respective gas sources of the semiconductor raw material gas and the dopant gas through MFC 26 and 28, the common gas pipe 22 and the six inlet ports 18a to 18f. 
At this time, not only are flow rates of H2 gas as a carrier gas, the semiconductor raw material gas and the dopant gas controlled individually and precisely by MFC 24, 26 and 28, respectively, but the gases are also mixed after the individual control and introduced into the reaction chamber 10 as a process gas having the raw material gas and the dopant gas of respective constant concentrations with almost no diffusion in a width direction through the six inlet ports 18a to 18f disposed in a width direction of the reaction chamber 10.
The process gas introduced into the reaction chamber 10 passes over the main surface of the silicon single crystal substrate 12 placed horizontally on the susceptor 14 rotating about the rotary shaft 16 as a center in one direction and in almost parallel to the main surface. During the passage over the main surface, a chemical reaction arises to grow the silicon single crystal thin film 32 in vapor phase on the main surface of the silicon single crystal substrate 12.
In a case where a silicon single crystal thin film 32 was formed on the main surface of the silicon single crystal substrate 12 using the conventional horizontal, single wafer vapor phase growth apparatus shown in FIGS. 5 and 6 as described above, and when the diameter of a silicon single crystal substrate 12 was 200 mm or less, a resistivity distribution along a diameter of the silicon single crystal thin film 32 formed on a main surface of the silicon single crystal substrate 12 was almost uniform.
However, when a dopant concentration of the silicon single crystal substrate 12 was relatively as low as of the order of 1015 atoms/cm3 and the diameter of a silicon single crystal substrate was 200 mm or more, for example a diameter of as large as 300 mm, it was found that there was a problem since a slip dislocation was generated in a peripheral region of a silicon single crystal thin film 32 with ease. If an integrated circuit is fabricated in a region with slip dislocation generated, leakage of a current in the circuit occurs problematically.
The following are conceived as a cause for generation of slip dislocation: That is, in a cold-wall vapor phase growth apparatus, when a silicon single crystal substrate 12 is heated by a uniform heating power, there arises a tendency that a temperature along a peripheral portion of the silicon single crystal substrate 12 is lower than a temperature in the central portion under an influence of a thermal condition that the outer wall surface of the reaction chamber 10 is forcibly cooled by a coolant. Such a tendency becomes conspicuous in a case of a diameter as large as 300 mm, a temperature difference between a peripheral portion and a central portion of a silicon single crystal substrate becomes large enough to generate slip dislocation.
Therefore, it is conceived that in order to prevent generation of slip dislocation in a peripheral portion of a silicon single crystal thin film 32, a power heating the peripheral portion of the silicon single crystal substrate 12 is regulated so as to be higher than that heating the central portion and reduce a temperature difference between the peripheral portion and the central portion so as to be smaller. With such regulation of heating powers, however, a resistivity of the peripheral portion of the silicon single crystal thin film 32 is deviated from that of the central portion thereof, a problem again arises, since a resistivity distribution along a diameter of the silicon single crystal thin film 32 becomes non-uniform.
In order to improve non-uniformity of a resistivity distribution along a diameter of a silicon single crystal thin film 32, it is only required that a flow rate of a dopant gas supplied onto a main surface of a silicon single crystal substrate 12 is varied and adjusted along a width direction of the reaction chamber 10.
However, since in the conventional horizontal, single wafer vapor phase growth apparatus shown in FIGS. 5 and 6, only a dopant gas of the same concentration is supplied into the reaction chamber 10 through a plurality of inlet ports 18a to 18f disposed in a width direction of the reaction chamber 10 and a concentration of the dopant gas cannot be changed in the width direction of the reaction chamber 10, therefore there can be performed no adjustment to alleviate non-uniformity of a resistivity distribution along a diameter of the silicon single crystal thin film 32.
In light of such circumstances, a trial was conducted that dopant gas flow rate regulating valves were provided at upstream sites from the respective inlet ports 18a to 18f to individually adjust a dopant gas flow rate at each inlet port 18a to 18f. However, according to this method, since a dopant flow rate is necessary to be adjusted at each inlet port 18a to 18f, a problem has arisen since actual adjustment of the dopant gas flow rates is very complex and non-realistic.
The invention has been made in light of the above described problems and it is accordingly an object of the invention to provide not only a semiconductor wafer obtained by forming a semiconductor thin film with uniform resistivity and virtually no slip dislocation therein on a main surface of a semiconductor single crystal substrate of a relatively low dopant concentration, as large as 300 mm or more in diameter but also a vapor phase growth apparatus by means of which a semiconductor thin film with uniform resistivity and substantially no slip dislocation therein can be formed on a main surface of a semiconductor single crystal substrate as large as 300 mm or more in diameter.
The above described task can be achieved by a semiconductor wafer relating to the invention and by means of a method for producing the semiconductor wafer.
That is, a semiconductor wafer relating to the invention is characterized by that the semiconductor wafer has a construction in which a semiconductor thin film with a resistivity distribution along a diameter within xc2x13%, both limits being included, is formed on a main surface of a semiconductor single crystal substrate of a dopant concentration ranging from 4xc3x971013 atoms/cm3 to 3xc3x971018 atoms/cm3, both limits being included, and a diameter ranging 300 mm to 400 mm, both limits being included.
In such a manner, a semiconductor wafer relating to the invention is constructed of a semiconductor single crystal substrate having a diameter as large as in the range of from 300 mm to 400 mm, both limits being included, of a dopant concentration as low as in the range of from 4xc3x971013 atoms/cm3 to 3xc3x971018 atoms/cm3, both limits being included and a semiconductor thin film with a resistivity distribution within xc2x13%, both limits being included, formed on a main surface of the semiconductor single crystal substrate with substantially no slip dislocation generated therein. Since, with a semiconductor wafer of the invention, requirements in terms of a large diameter and uniform resistivity on a recent semiconductor wafer are simultaneously achieved, use of the semiconductor wafer largely contributes to realization of increase in throughput and yield of semiconductor chip fabrication.
In a semiconductor wafer relating to the invention, it is preferable that a conductivity type of a semiconductor single crystal substrate is p and a resistivity thereof ranges from 0.03 xcexa9xc2x7cm to 300 xcexa9xc2x7cm, both limits being included. In this range of resistivity, a resistivity desirably ranges from 1 xcexa9xc2x7cm to 20 xcexa9xc2x7cm, both limits being included, from the viewpoint of actual fabrication of a semiconductor device using a semiconductor wafer. In this case, the use of boron as a dopant added to a semiconductor single crystal substrate is preferable in light of the practical aspects of handling in the use, easiness in controllability or the like needs.
In addition, in a semiconductor wafer relating to the invention, a diameter of a semiconductor single crystal substrate is preferably 300 mm in length. At the present stage, since a semiconductor single crystal substrate with a diameter up to 300 mm can be produced in a stable manner with high quality, in a case of a diameter as large as 300 mm, it is practically enjoyed to an full extent that a resistivity distribution of a semiconductor thin film along a diameter is achieved with uniformity of within xc2x13%, both limits being included, on a main surface of a semiconductor single crystal substrate whose dopant concentration ranges from 4xc3x971013 atoms/cm3 to 3xc3x971018 atoms/cm3, both limits being included.
Further, a semiconductor single crystal substrate is preferably a silicon single crystal substrate and a semiconductor thin film is preferably a silicon single crystal thin film. That is, a large diameter and a uniform resistivity are simultaneously achieved on a silicon single crystal wafer constituting the main stream of semiconductor wafers at the present time, and with this achievement, a semiconductor wafer of the invention is expected to find wide and various applications in semiconductor device fabrication.
Further, a vapor phase growth apparatus relating to the invention comprises a reaction chamber and a plurality of gas inlet ports disposed in a width direction of the reaction chamber, wherein a semiconductor raw material gas is supplied through the plurality of gas inlet ports onto a main surface of a semiconductor single crystal substrate rotating in the reaction chamber in one direction in almost parallel to the main surface thereof to grow a semiconductor thin film on the main surface thereof in vapor phase, and is characterized by that the vapor growth apparatus further comprises a main dopant gas pipe supplying a dopant gas to all of the plurality of gas inlet ports and an auxiliary dopant gas pipe supplying the dopant gas to a specific gas inlet port selected from the plurality of gas inlet ports. In such a manner, in a vapor phase growth apparatus relating to the invention, a main dopant gas pipe supplying a dopant gas to all of the plurality of gas inlet ports and an auxiliary dopant gas pipe supplying the dopant gas to a specific gas inlet port are simultaneously equipped. With such a construction, since it is possible that not only is the dopant gas supplied to a main surface of a semiconductor single crystal substrate in the reaction chamber through all of the gas inlet ports from the main dopant gas pipe to realize a vapor phase growth of a semiconductor thin film such that global resistivity of the thin film is controlled in the vicinity of a predetermined target value on the main surface of a semiconductor single crystal substrate, but the dopant gas is additionally supplied to the main surface of the semiconductor single crystal substrate in the reaction chamber through the specific gas inlet port from the auxiliary dopant gas pipe to adjust a resistivity distribution of a semiconductor thin film, therefore even when the semiconductor thin film is formed on the main surface of a large diameter semiconductor single crystal substrate, a uniform resistivity across the semiconductor thin film is ensured.
For example, a resistivity distribution along a diameter of a semiconductor thin film formed on a main surface of a semiconductor single crystal substrate with a diameter as large as in the range of from 300 mm to 400 mm, both limits being included, and a dopant concentration as low as in the range of from 4xc3x971013 atoms/cm3 to 3xc3x971018 atoms/cm3, both limits being included, can be within xc2x13%, both limits being included.
Further, after supplying conditions for a dopant gas supplied through the main and auxiliary dopant gas pipes are adjusted such that a resistivity distribution along a diameter of a semiconductor thin film is uniform within, for example, xc2x13%, both limits being included, even when a target resistivity of a semiconductor thin film becomes necessary to be altered higher or lower, a supply rate of hydrogen gas diluting the dopant gas is controlled while a ratio in flow rate of the dopant gas supplied through the main and auxiliary dopant gas pipes is retained and thereby, a change in target resistivity can be realized while uniformity of a resistivity distribution is maintained. Therefore, alteration of a target resistivity of a semiconductor thin film can be effected with ease and speediness, thereby achieving improved productivity.
Further, in a vapor phase growth apparatus relating to the invention, it is preferable that a plurality of gas inlet ports are grouped into three kinds of inlet ports: inner inlet ports disposed at the innermost side in a width direction of a reaction chamber, outer inlet ports disposed at the outermost side in the width direction of the reaction chamber and middle inlet ports each between one of the two inner inlet ports and the corresponding one of the two outer inlet ports, and a specific gas inlet port through which a dopant gas is supplied into the reaction chamber from an auxiliary dopant gas pipe is one or two kinds selected from the group consisting of the inner inlet ports, the outer inlet ports and the middle inlet ports.
In such a manner, in a vapor phase growth apparatus relating to the invention, a plurality of gas inlet ports are grouped into three kinds of inlets including the inner inlet ports, the outer inlet ports and the middle inlet ports and a specific gas inlet port through which a dopant gas is supplied into the reaction chamber from an auxiliary dopant gas pipe is one or two kinds selected from the group consisting of the inner inlet ports, the outer inlet ports and the middle inlet ports. With such a construction, the dopant gas can be supplied through the inner inlet port only, through the outer inlet ports only or through the middle inlet port only, or through the inner inlet ports and the middle inlet ports combined or through the middle inlet ports and the outer inlet ports combined.
That is, on one hand, a dopant gas supplied through the gas inlet ports of three kinds including the inner inlet ports, the outer inlet ports and the middle inlet ports into the reaction chamber from the main dopant gas pipe is directed toward points in the vicinity of the center of a main surface of a semiconductor single crystal substrate from the inner gas inlet ports, toward points in the vicinity of the outer periphery of the semiconductor single crystal substrate from the outer gas inlet ports and toward points between the central portion and the outer peripheral portion of the main surface of the semiconductor single crystal substrate from the middle gas inlet ports, on an imaginary central axis passing through the center of the main surface of the semiconductor single crystal substrate in a width direction of the reaction chamber, while on the other hand, the dopant gas can be additionally supplied into the reaction chamber from an auxiliary dopant gas pipe through a specific gas inlet port corresponding to a local region with high resistivity of a semiconductor thin film grown in vapor phase on the main surface of the semiconductor single crystal substrate, the specific gas inlet being one or two kinds selected from the group consisting of the inner inlet ports, the outer inlet ports and the middle inlet ports.
In such a manner, a dopant gas supplied all over a main surface of a semiconductor single crystal substrate through all of the gas inlet ports of the three kinds from a main dopant gas pipe and the dopant gas supplied locally to the main surface of the semiconductor single crystal substrate into the reaction chamber through a specific gas inlet port of one or two kinds selected from the group consisting of the inner inlet ports, the outer inlet ports and the middle inlet ports from an auxiliary dopant gas pipe are combined so as to make uniform resistivity of a semiconductor thin film formed on the main surface of a semiconductor single crystal substrate.
It should be noted that while description is made of the case where a plurality of gas inlet ports disposed in a width direction of the reaction chamber include the three kinds of the inner inlet ports, the outer inlet ports and the middle inlet ports, gas inlet ports of more than three kinds can be equipped according to a level of development in large diameter of a semiconductor single crystal substrate. In that case, a specific gas inlet port through which a dopant gas is supplied into the reaction chamber from an auxiliary dopant gas pipe may be any one kind selected from more than three kinds of gas inlet ports or any combination of two or more kinds selected from the more than three kinds of gas inlet ports.
Further, in a vapor phase growth apparatus relating to the invention, it is more preferable that the main dopant gas pipe and the auxiliary dopant gas pipe are equipped with respective dopant gas flow rate regulators regulating supply of the dopant gas.
In such a manner, in a vapor phase growth apparatus relating to the invention, the main dopant gas pipe and the auxiliary dopant gas pipe are equipped with respective dopant gas flow rate regulators regulating supply of the dopant gas. With this construction, since it is possible that not only is a dopant gas supplied all over a main surface of a semiconductor single crystal substrate in the reaction chamber through all of the gas inlet ports from the main dopant gas pipe and the dopant gas is additionally supplied locally onto the main surface of the semiconductor single crystal substrate through the specific gas inlet port from the auxiliary dopant gas pipe are separately controlled to adjust a resistivity distribution of a semiconductor thin film to high precision, therefore even when the semiconductor thin film is formed on the main surface of a large diameter semiconductor single crystal substrate, a more uniform resistivity distribution along a diameter of the semiconductor thin film is achieved.
It should be noted that in a case where an auxiliary dopant gas pipe is constructed of two kinds of dopant gas pipes, the dopant gas pipes are desirably equipped with respective dopant gas flow rate regulators. With such provision of the regulators, a resistivity distribution along a diameter of a semiconductor thin film becomes more uniform.
Further, a vapor phase growth apparatus relating to the invention in the above described example is preferably a cold-wall vapor phase apparatus. In this case, since the outer wall surface of the reactor chamber is forcibly cooled by a coolant, deposits to be attached on the inner wall surface of a reaction chamber in vapor phase growth is prevented from occurring, thereby forming a higher quality semiconductor thin film.